1. Field of the Invention
The present invention relates to an apparatus for driving a printhead and a method of driving the printhead.
2. Description of the Related Art
One conventional printhead is a piezoelectric printhead. A piezoelectric material is polarized and then formed with a plurality of grooves therein that define ink pressure chambers. The walls that define the grooves are formed with electrodes thereon. When drive voltages are applied to the electrodes, the walls are deformed to introduce ink into the ink pressure chambers from an ink reservoir and then pressurize the ink held in the ink chambers, so that ink drops are ejected through orifices onto a print medium.
With the conventional printhead, a suction operation should be performed periodically in order to maintain the orifices not clogged. Printing cannot be performed during suction operation. Therefore, performing a suction operation is an obstacle to increasing the throughput of a printer. Ink of about several micro liters is wasted during suction operation. The amount of wasted ink increases with increasing number of times of suction operation.
The present invention was made in view of the aforementioned drawbacks of the prior art ink jet printer.
An object of the invention is to provide an apparatus for driving a printhead and a method of driving the printhead. The apparatus and method prevent poor, insufficient ejection of ink drops, increase the throughput of the printer, and reduce the amount of wasted ink.
An apparatus for driving a printhead comprises a timer, power supply, and a controller. The power supply applies a drive voltage to the printhead to eject ink drops from the printhead. The timer counts an elapsed time during which the printhead does not eject ink drops. The controller performs an ejection test where the drive voltage drives the printhead a plurality of times to eject a plurality of ink drops. The controller drives the power supply to increase the drive voltage in accordance with a length of the elapsed time.
The ejection test is performed after a predetermined length of the elapsed time. The drive voltage and the predetermined length of the elapsed time are selected in accordance with a decrease in an ejection speed of the ink drops.
The controller controls the drive voltage such that the surface of meniscus of ink in the orifice is subjected to fine vibration before the ink drop is ejected.
The surface of the meniscus is subjected to fine vibration prior to a printing operation and an ejection test.
When the ejection test is performed, the controller determines the drive voltage by adding a first correction voltage to a drive voltage required for a printing operation.
When the surface of meniscus is subjected to fine vibration, the controller determines the drive voltage by adding a second correction voltage to the drive voltage required for the printing operation.
A method of driving a printhead comprises the steps of:
driving the printhead to eject ink drops through orifices of the printhead to perform a printing operation when print data is received;
counting an elapsed time during which the printing operation is not performed; and
performing an ejection test in which the printhead is driven in accordance with a length of the elapsed time.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.